The centOS box has a dhcp server running. Currently it is handing out IP address on 192.168.3.0/24 but I don't think DNS is working correctly either. I have two boxes 192.168.3.5 and 192.168.3.6 that can ping each other all day but nslookup raid_array will not work. Here is my setup right now.

I want all 192.168.3.0/24 traffic to forward over eth0. Any traffic headed for the internet should be masqueraded as the 172.16.0.72 over eth1. Where does DNS fit into this?

BTW, in your ifcfg-eth1 file, change the device name to eth1, otherwise you may have problems.

DNS is there to provide domain name <=> ip addressing, you might need to have your own DNS server if you have servers inside the 192.168.3.X network, so you do not have to remember IP addresses, though you will want to configure those machines with static IPs or set up DHCP to always assign them the same IP. If however you do not have a need for internal DNS, use the ones your ISP provides, or google's (8.8.8.8).